In microscopy, it is frequently desired to be able, without major conversion, to use an available reflected-light microscope for the purpose of observing light-transmitting objects. This desire is particularly great in the field of microphotometry where the transfer from reflected-light photometry to transmitted-light photometry involves major conversion and adjustment tasks. Thus, as a rule, the installed monochromator which serves the illumination-beam path must be converted, or a second monochromator must be provided.
In microscopy on light-transmitting objects, a known optical system is provided with a retroreflection device for light emanating from an incident-light illuminating device and transmitted by the object, the light being reflected back onto the rear side of the object. The present invention relates to such a system, as described, for example, in British Pat. No. 784,822. To retroreflect the light transmitted by the object, the known device has a multi-tetrahedral mirror, located below the object, to depolarize polarized light from the incident-light illuminating device. A transmitted-light image of the object illuminated with incident illumination is obtained, by using a crossed-polarization analyzer in the path of the observation beam, thereby permitting through-passage of only the depolarized portion of light coming from the tetrahedral mirror.
The known device, however, gives a relatively dark, low-contrast image, and it is not suitable for photometric measurements.
From West German published patent application OS No. 2,546,079, a reflecting condenser for microscopes is known to employ two spherical or aspherical annular mirrors to reflect the rays of an incident-light bright-field illumination, the object-reflected rays being transmitted back as transmitted-light dark-field illumination onto the object. Such a device is admittedly suitable for incident-light fluorescence microscopy but not for transmitted-light photometry.